More chemistry in small spaces.

Abstract

This Account is about coaxing molecules into spaces barely big enough to contain them:
encapsulation complexes. In capsules, synthetic modules assemble to fold around their
molecular targets, isolate them from the medium for relatively long times, place them
in a hydrophobic environment, and present them with functional groups. These arrangements
also exist in the interior spaces of biology, and the consequences include the familiar
features of enzymes: rapid reactions, stabilization of reactive intermediates, and
catalysis. But inside capsules there are phenomena unknown to biology or historical
chemistry, including new structures, new stereochemical relationships, and new reaction
pathways. In encapsulation complexes, as in architecture, the space that is created
by a structure determines what goes on inside. There are constant interactions between
the container and contained molecules: encounters are not left to chance; they are
prearranged, prolonged, and intense. Unlike architecture, these reversibly formed
containers emerge only when a suitable guest is present. The components exist, but
they cannot assemble without anything inside. Modifications of the capsule components
give rise to the results of the present Account. The focus will be on how seemingly
small changes in the encapsulation complexes, exchanging a C═S for a C═O, reducing
an angle here and there, or replacing a hydrogen with a methyl, can lead to unexpectedly
large differences in behavior.